From ancient Greek, "For the most beautiful one", or "To the prettiest one."
It is spelt in most Discordian texts as καλλιστι, although most copies of the Principia Discordia spell it as καλλιχτι, although this is incorrect - the reason behind this is given by Gregory Hill as being due to the Greek characters being not properly aligned with the Roman characters on the keys.
καλλιστι is what was written on the apple that Eris threw into the gods' party on Mount Olympus, because she was pissed off they hadn't invited her. 3 of the goddesses present started arguing about who it was to (actually, there were 5 goddesses, but the Greeks didn't know the law of fives). Zeus decreed that Paris was to decide who was the fairest. The goddesses then proceeded to go and bribe him. Hera offered to make him king of Europe and Asia, Athena offered wisdom and skill in war, and Aphrodite (who cheated, because she used cherubs and shit) offered the love of the world's most beautiful woman. Naturally, because he was a dirty pervert, Paris chose the Aphrodite's offer. She won and he got laid. The only problem was that this woman happened to be the Greek king Menelaus' wife, Helen. Naturally, he got pissy, and declared war on Troy, where Paris lived. This is called the Doctrine Of The Original Snub, and is a huge reason not to fuck with Eris.